1. Background of the Invention
This invention relates to an inexpensive yet accurate measurement of flatness of aluminum sheet used in the manufacture of containers.
2. Background Art
In the manufacture of aluminum containers, such as aluminum beverage cans and ends therefor, it is necessary for the proper function of the end making apparatus to use flat sheet stock as the feed material. Since the sheet stock is produced in a rolling mill, a certain amount of curvature or buckling may be present. It is, therefore, necessary to measure the amount of such curvature or undulations to determine whether the maximum permissible buckles have been exceeded.
Such measurements may be made on a random sampling basis or, in some instances, on each sheet. In either instance, it is desirable that the measurement be made quickly and inexpensively, yet accurately.
Conventionally, this measurements is made by placing the sheet to be measured on a carefully machined flat surface and then placing a long straight edge across adjacent high points. The depth of the low point is then measured using a ruler or a step gauge.
However, it has been found that the weight of the straight edge may compress the sheet slightly, thus leading to inaccuracy in the measurement. Furthermore, measurement with a ruler, or even a step gauge, may be less than totally accurate as well as requiring additional amount of time, particularly if sufficient care is taken to provide some asurance of accuracy.